This invention relates generally to gas generant materials, such as those used to inflate automotive inflatable restraint airbag cushions and, more particularly, to burn rate-enhanced gas generant compositions and methods.
Gas generating chemical compositions and formulations are useful in a number of different contexts. One significant use for such compositions is in the operation of automotive inflatable restraint airbag cushions.
It is well known to protect a vehicle occupant using a cushion or bag, e.g., an "airbag cushion," that is inflated or expanded with gas when the vehicle encounters sudden deceleration, such as in the event of a collision. In such systems, the airbag cushion is normally housed in an uninflated and folded condition to minimize space requirements. Upon actuation of the system, the cushion begins to be inflated or expanded, in a matter of no more than a few milliseconds, with gas produced or supplied by a device commonly referred to as an "inflator." The airbag cushion is designed to inflate into a location within the vehicle between the occupant and certain parts of the vehicle interior, such as the doors, steering wheel, instrument panel or the like, to prevent or avoid the occupant from forcibly striking such parts of the vehicle interior. As a consequence, nearly instantaneous gas generation is generally desired and required for the effective operation of such inflatable restraint installations.
Various gas generant compositions have heretofore been proposed for use in vehicular occupant inflatable restraint systems. Gas generant compositions commonly utilized in the inflation of automotive inflatable restraint airbag cushions have previously most typically employed or been based on sodium azide. Such sodium azide-based compositions, upon initiation, normally produce or form nitrogen gas. While the use of sodium azide and certain other azide-based gas generant materials meets current industry specifications, guidelines and standards, such use may involve or raise potential concerns such as involving the safe and effective handling, supply and disposal of such gas generant materials. Thus, there remains need for safe, effective improved gas generants such as composed of a fuel material and an oxidizer therefor such as upon actuation react to form or produce an inflation gas for inflating vehicular safety restraint devices.
Basic copper nitrate (Cu(NO.sub.3).sub.2 .cndot.3Cu(OH).sub.2) (sometimes referred to herein by the notation "bCN") has or exhibits various properties or characteristics including, for example, high gas output, density and thermal stability and relatively low cost such as to render desirable the use or gas generant composition inclusion thereof as an oxidizer. The use of such basic copper nitrate or related materials has been the subject of various patents including Barnes et al, U.S. Pat. No. 5,608,183, issued Mar. 4, 1997 and Barnes et al, U.S. Pat. No. 5,635,688, issued Jun. 3, 1997, the disclosures of which are fully incorporated herein by reference.
In practice, it is generally desired or required that the inflators of inflatable restraint systems be able to supply or provide inflation gas in predetermined mass flow rates. The gas mass flow rate resulting upon the combustion of a gas generant composition is typically a function of the surface area of the gas generant undergoing combustion and the burn rate thereof.
A limitation on the greater or more widespread use of basic copper nitrate in such gas generant compositions is that basic copper nitrate-containing gas generant compositions may exhibit or otherwise have associated therewith undesirably low or slow burn rates. In practice, the normal or typical burn rates associated with such gas generant compositions can act to restrict the use of such gas generant compositions to those applications wherein faster burn rates are either not required or desired. For example, such low or slow burn rate compositions may be unsuited for various side impact applications where more immediate generation or supply of inflation gas may be required or desired.
Further, as will be appreciated, various factors, such as including mechanical properties such as strength, may serve to limit or restrict the ability to tailor, change or otherwise alter the shape or geometric form of a gas generant material. Thus, gas generant materials having higher burn rates may permit greater freedom with regard to the shape or form of the gas generant employed.
In addition, for basic purposes such as improved reliability, it is generally desired that at least certain performance characteristics of gas generant materials, e.g., burn rate, be largely independent of ambient conditions such as pressure, for example.
In general, the burn rate for a gas generant composition can be represented by the equation (1), below: EQU Rb=Bp.sup.n (1)
where,
Rb=burn rate (linear) PA1 B=constant PA1 P=pressure PA1 n=pressure exponent, where the pressure exponent is the slope of the plot of the log of pressure along the x-axis versus the log of the burn rate along the y-axis PA1 a fuel component, PA1 a basic copper nitrate oxidizer component therefor, and PA1 a metal oxide burn rate enhancing additive component comprising at least one oxide of a metal selected from the group consisting of Al, Ti, Zn, Mg and Zr, in sufficient amount wherein upon ignition of the gas generant composition, the gas generant composition burns at an increased rate as compared to a similar composition without the inclusion of said metal oxide burn rate enhancing additive. PA1 about 30 to about 60 weight percent of a gas generating fuel, PA1 about 40 to about 65 weight percent of a basic copper nitrate oxidizer, and PA1 about 2 to about 10 weight percent of a burn rate enhancing and slag formation additive including about 0.5 to about 5 weight percent of at least one oxide of a metal selected from the group consisting of Al, Ti, Zn, Mg and Zr and about 0.5 to about 5 weight percent of silica.
As will be appreciated, the pressure exponent generally corresponds to the performance sensitivity the respective gas generant material, with lower burn rate pressure exponents corresponding to gas generant materials which desirably exhibit corresponding lesser or reduced pressure sensitivity.
Further, the reduction in either or both the amount and concentration of particulate material that may issue forth from an inflator device upon the actuation thereof has been one focus of continuing improvement efforts with regard to inflatable restraint systems. In particular, there is a need and a demand for gas generant compositions which avoid the need for more extensive or complicated than would otherwise be desired particulate removal means in or associated with an inflator device. As will be appreciated, such extensive or complicated removal means may suffer from one or more disadvantages relating to size, weight and cost.
Unfortunately, various basic copper nitrate-containing gas generant compositions may, upon combustion, produce or result in non-gaseous combustion products which exhibit undesirably poor slagging properties or characteristics. As a result, the use of such basic copper nitrate-containing gas generant compositions may necessitate or require the use of expensive filtration devices or techniques in or in association with corresponding inflator devices.
Thus, there is a need and a demand for gas generant compositions and related methods which while containing basic copper nitrate as a component thereof provide sufficiently high or elevated burn rates. Further, there is a need and a demand for such gas generant compositions and related methods wherein non-gaseous combustion products are of a form which permits the ready removal thereof without necessitating costly or complicated removal devices or techniques.